This invention relates to methods for treating one or more layers in a multilayer golf ball to facilitate bonding therebetween, and the resultant golf balls prepared with the treatment of a layer therein.
Golf balls are typically divided into two general types or groups: a) solid golf balls and b) wound balls. The difference in play characteristics resulting from these different types of constructions can be quite significant. Solid golf balls may be one-piece or multilayer, while wound balls always have at least three layers of at least a center, wound layer, and a cover.
Solid golf balls having a two-piece construction are generally most popular with the recreational golfer because they provide a durable ball capable of achieving long distances in play. Two-piece balls are typically made with a single solid core, usually formed of a crosslinked rubber, which is encased by a cover material. Typically the solid core is made of polybutadiene chemically crosslinked with a metal salt of an unsaturated fatty acid and/or similar crosslinking agents. Covers typically are ionomers and blends of ionomers with other thermoplastics, such as SURLYN(copyright) resins, which are ionomer resins sold commercially by E. I. DuPont de Nemours of Wilmington, Del., or IOTEK(copyright), which is sold commercially by Exxon Corporation.
Solid golf balls having three or more layers are more expensive to produce, but often provide improved playing characteristics. Such balls typically have a rubber-based spherical center around which is concentrically disposed one or more intermediate layers, also known as mantle layers. One or more cover layers are typically disposed concentrically about the intermediate layer(s) similar to two-piece golf balls.
Wound balls typically have either a solid or liquid filled center around which a tensioned elastomeric material (i.e., a stretched elastic thread) is wound to form a core. The wound core is then covered with a cover material, which may be the same as those discussed above for solid golf balls but also typically include balata (trans-polyisoprene) and urethanes. However, like three-piece multilayer solid golf balls, the more complex structure of wound balls generally results in a longer manufacturing time and greater expense in the production thereof compared to a two-piece ball.
One difficulty common to preparing solid multilayer balls is that materials of an outer layer do not necessarily bond well with the materials used in the inner layer(s). This can result in layer separation, particularly when the golf ball is struck by a club, which can detrimentally affect the playability and appearance of the golf ball. Moreover, should the cover be cut or damaged, improper bonding between layers tends to permit further degradation of the cover or even complete disintegration of the ball layers.
Various types of surface treatment techniques are known for use in modifying polymer surfaces. These techniques include mechanical abrasion; chemical abrasion, such as etching; and high-voltage electrostatic discharge, also known as corona treatment. See, e.g., U.S. Pat. No. 5,466,424 (corona discharge surface treating method) and Stobbe, Bruce, xe2x80x9cCorona Treatment 101,xe2x80x9d Label and Narrow Web Indus., May-June, 1996.
One method of modifying polymer surfaces is plasma treating. Plasma treatment of various shapes and types of polymers in general is well known. See, e.g., Kaplan, S. L., xe2x80x9cCold Gas Plasma Treatment for Re-Engineering Films,xe2x80x9d Paper Film Foil Converter, 71(6) June, 1997; Rose, P., et al., xe2x80x9cTreating Plastic Surfaces with Cold Gas Plasmas,xe2x80x9d Plastics Engineering, pp. 41-45 (October, 1985). Plasma treatment generally oxidizes the surface of a material being treated. For example, U.S. Pat. No. 5,387,842 discloses a steady-state, glow discharge plasma generated within the volume between a pair of parallel, insulated metal plate electrodes spaced up to 5 cm apart and RF energized with an rms potential of 1 to 5 KV at 1 to 100 KHz. The electrodes are disclosed to be located within an enclosure capable of maintaining an atmosphere other than atmospheric air, such as a noble gas, between the electrode surfaces. See also U.S. Pat. No. 5,316,739 and U.S. Pat. No. 5,098,483 (methods of treating spherical surfaces).
U.S. Pat. No. 5,414,324 discloses a similar parallel plate apparatus and process, but charges the electrodes with an impedance matching network adjusted to produce a stable, uniform glow discharge at atmospheric pressure, which is also known as corona discharge.
U.S. Pat. Nos. 5,403,453 and 5,456,972 disclose polymer materials, such as film and fabrics, that may be non-destructively surface treated to improve water wettability by exposure to a glow discharge plasma sustained at substantially atmospheric pressure in a modified gas atmosphere of helium or argon.
U.S. Pat. No. 4,919,434 discloses a golf ball having a cover which includes an inner cover layer and an outer cover layer, each of which includes a thermoplastic resin. Preferably, the layers are formed of materials capable of fusion bonding with each other to properly adhere the layers together.
JP Patent Document No. 60215374 discloses a golf ball made of synthetic resin, wherein the golf ball cover surface is subjected to microwave plasma treatment to improve the thin coating layer""s peeling resistance against shock or flexing fatigue. This process is disclosed as greatly reducing treatment time from 10 to 24 hours down to several minutes.
U.S. Pat. No. 4,613,403 discloses a method for treating a golf ball surface made of balata resin, thermoplastic elastomer, ionomer resin, or the like with unpolymerizable gas plasma and subsequently applying the usual coating in an apparatus adapted to expose the surface of the ball to the plasma. The process is alleged to make the coating on the golf ball hard-exfoliative, i.e., more mar-resistant.
U.S. Pat. No. 5,286,532 discloses a method for producing golf balls by surface-treating the golf ball with atmospheric pressure plasma prior to finish coating to provide a good adhesion of the coating to the golf ball, which coating is highly resistant to discoloration and deterioration.
However, these references do not disclose methods for treating one or more internal layers within a multilayer ball, i.e., other than on the surface, to provide golf balls having improved durability and acceptable playing characteristics, such as low driver spin and high initial velocity. It is thus desirable to provide a method capable of producing such multilayer golf balls, which golf balls themselves are also novel.
The invention relates to a golf ball including a core having an outer surface that is sufficiently treated to increase adhesion thereof and a cover layer having a thickness of at least about 0.007 inches and a plurality of dimples, wherein the cover layer is disposed concentrically about the core and bonded to the core at the treated surface and the golf ball is substantially free of adhesive. In particular, the surface is treated by exciting a gas to a plasma state and applying the gas to the surface being treated under sufficient conditions to increase the adhesion capability of the surface to enhance or facilitate bonding with an adjacent layer. The surface may also be treated by chemical means, such as etching, to increase adhesion capability.
In one embodiment, the invention relates to a golf ball including a core having a corona-discharge treated outer surface to increase adhesion thereof to an adjacent layer and a cover layer having a thickness of at least about 0.007 inches and a plurality of dimples, wherein the cover layer is disposed concentrically about the core and bonded to the core at the treated outer surface.
In another embodiment, the present invention relates to a golf ball including a core having a plasma-treated surface and a cover layer having a thickness of at least about 0.007 inches and having a plurality of dimples, wherein the cover layer is disposed concentrically about the core and is bonded to the core. Plasma treatment includes at least one of low pressure plasma treatment or corona-discharge treatment, the latter of which is typically conducted at or around atmospheric pressure. It should be understood that any of these types of surface treatment may be used with any of the following embodiments.
Optionally, but preferably, the cover layer is disposed about the core without need for an adhesive between the core and cover layer. In one embodiment, the ball contains three or more layers; it should be understood that the cover layer having dimples is disposed over a core made of two or more layers. Thus, what is often called an xe2x80x9cinner cover layerxe2x80x9d in golf balls having a core and a cover layer including an inner cover layer and an outer cover layer should be understood herein to be the outermost layer of the core about which a cover layer having dimples is disposed.
As used herein, the terms xe2x80x9ccoverxe2x80x9d and xe2x80x9ccover layerxe2x80x9d refer to the outermost layer of a golf ball that contains dimples. Any desired type of coating, such as paint, lacquer, or the like, may be disposed about the cover layer, i.e., about the golf ball, in any manner known to those of ordinary skill in the art. As used herein, the term xe2x80x9ccorexe2x80x9d means the one or more layers of a golf ball about which the cover layer is disposed. As used herein, the outer, and in particular the outermost, core layers may be comprised of either thermoset rubber compositions, thermoplastic resins, or the like.
In one embodiment, the core has a single layer. In another embodiment, the core includes a center and an intermediate layer disposed about the center. Any number of optional intermediate layers may also be disposed between the center and cover layer. In a preferred embodiment, the core includes a center and at least one intermediate layer disposed about the center, with the outermost intermediate layer being treated, e.g., by low pressure plasma treatment or corona discharge treatment, to facilitate adhesion of the cover layer to the core. In a more preferred embodiment, there are two intermediate layers.
In another embodiment, the core includes a center, and at least one intermediate layer disposed about the center, wherein at least one intermediate layer is treated to facilitate bonding to the adjacent layer. Preferably, the intermediate layer adjacent the cover layer is treated to facilitate bonding between the outermost intermediate layer of the core and the cover. In another embodiment, at least one of the intermediate layers includes a material having a flex modulus of about 50,000 psi and the cover layer has a thickness of less than about 0.045 inches and includes at least one of a thermoset material or a thermoplastic material. In a preferred embodiment, the cover layer has a thickness of from about 0.014 to 0.04 inches.
In yet another embodiment, the cover layer has a Shore D hardness of less than about 75. In a preferred embodiment, the cover layer has a Shore D hardness of between about 40 to 65. In another embodiment, at least one of the intermediate layers and the cover layer has a flexural modulus of about 50,000 psi to 120,000 psi. In another embodiment, the treated surface includes a material having a surface energy from about 40 dyne/cm2 to 70 dyne/cm2. In another embodiment, the intermediate layer adjacent to the cover layer has a Shore D hardness of at least about 50. In a preferred embodiment, the intermediate layer has a Shore D hardness of about 65 to 74.
In one embodiment, the cover includes any suitable material known to those of ordinary skill in the art, such as a thermoset material as noted above that is selected from the group of polyisoprene, polybutadiene, polyurethane, polysulfide rubber, polyurea, polyester, epoxy resin, and mixtures thereof. In a preferred embodiment, the cover includes a thermoplastic material of a material selected from the group of a polyolefin, polyamide, polyester, polytrimethylene terephthalate, copoly(ether-ester), copoly(ester-ester), polyamide, copoly(urethane-ester), copoly(urethane-ether), polyacrylate, polystyrene, styrene-butadiene-styrene copolymer, styrene-ethylene-butylene-styrene copolymer, polypropylene, ethylene-propylene-diene terpolymer or ethylene-propylene vulcanized copolymer rubber, polycarbonate, and mixtures thereof.
In another embodiment, the intermediate layer most closely adjacent to the cover includes an ionomer resin, a polyurethane, a polyetherester, a polyetheramide, a polyester, a vulcanized elastomer, a functionalized styrenebutadiene elastomer, a metallocene polymer, a polyamide, or acrylonitrile butadiene-styrene copolymer, or a blend thereof.
In one embodiment, an outer diameter of the intermediate layer adjacent to the cover layer is less than about 1.666 inches. In another embodiment, the core includes a center and at least two intermediate layers disposed progressively concentrically about the center. In yet another embodiment, the center may be solid, hollow, or fluid-filled. In another embodiment, at least one intermediate layer includes a length of tensioned elastomeric material. In one embodiment, the golf ball is substantially free of adhesive between the cover and the treated surface.
The invention also encompasses a golf ball including a core having a center layer and at least two intermediate layers disposed concentrically about the center layer, and a cover disposed concentrically about the core, wherein at least one of the core layers is treated at an interface with an adjacent layer that is bonded thereabout.
The golf balls of the invention may be prepared, for example, by forming at least one layer of a golf ball, treating an outermost surface of the at least one layer at a pressure, and bonding at least a portion of a cover layer concentrically about the at least one layer so as to form a cover layer having a thickness of at least about 0.007 inches and a plurality of dimples. In a preferred embodiment, the treating is accomplished by applying a gas excited to a plasma state to the surface being treated. In a more preferred embodiment, the gas is excited to the plasma state by RF energy, electron beam, microwave, electrical discharge, or other suitable methods known to those of ordinary skill in the art. Indeed, a primary or secondary method may be used. Primary methods include those where the surface to be treated is placed in the plasma field, while secondary methods include those where the plasma is blown or otherwise moved onto the surface to be treated.
In a preferred embodiment, the pressure at which the plasma treatment is conducted is below atmospheric pressure. In another embodiment, the at least one layer includes a core. In a preferred embodiment, the core includes a center and at least one treated intermediate layer disposed about the center. In a more preferred embodiment, the at least one layer further includes a second intermediate layer disposed outwardly adjacent to a treated first intermediate layer. In another embodiment, the second intermediate layer is also treated and is disposed between the center and the treated first intermediate layer.
In one embodiment, the portion of the cover material bonded to the treated layer includes a thermoset material. In another embodiment, the portion of the cover material is formed by casting a reactive liquid material or by compression or injection molding, but preferably is formed by casting. In yet another embodiment, the method further includes mechanically abrading at least a portion of an outermost surface of at least one layer. In another embodiment, the at least one layer has a surface energy of less than about 50 dyne/cm2 before treating. In a preferred embodiment, the layer that is treated and the adjacent layer bonded thereto include different materials.